what is the temperature underground? i am trying to prove that on
average it is cooler below the ground than above...except for obvious
exceptions where the temperature outside is cold enough to snow. this
topic came up at dinner last night when i asked why it was that i
cannot get cool water from my faucets at home. my friend replied,
"because it is warm underground so the water gets warm." we live in
san diego where the temperature on average is from 65-75 during the
day and 50-60 at night.

The main point about temparatures below ground is that they are
relatively stable or constant compared to the daily and seasonal
variations of above ground temperatures because of the insulating
effect of the ground itself. (Very slow to warm up and very slow to
cool down.)
The deeper you go, the further from the surface, the more constant the
temperature compared to the surface air variation. Air heats up and
cools down quickly compared to bodies of water and soil and rock heats
and cools slowest of the 3. At greater depths however temperatures,
while stable, gradually increase and at the great depths some of our
deep mines and drill holes are reaching the temperatures considerably
above 50-55 as we get closer to the molten inner core of the planet.
The insulating effect of the ground contributes to making the air in
working mines very hot because the heat generated in the mining
activities does not dissipate very fast from the mine air into the
surrounding rock and so ventilation is required to remove the hot air
as well as maintaining oxygen levels.
Apparently 50-55 Fahrenheit at about 4 feet is considered average,
however over sufficient time periods (years) the temperature can
settle at lower (or higher) temperatures. "Permafrost" which
apparently covers about 20% of the earths surface is soil at or below
freezing and over sufficient time periods can extend to hundreds of
metres below the surface.
See: http://en.wikipedia.org/wiki/Permafrost
or: http://www.alyeska-pipe.com/Pipelinefacts/Permafrost.html
Animals, in both hot and cold climates, often burrow to reach the
stable cooler or warmer areas respectively, compared to above ground
air temperatures. It is better, for example, to live at a constant
50-55 below ground in a desert than to live exposed on the surface and
suffer temeratures that may vary from below 0 to over 120 in the
course of every 24 hours.
Below ground cellars may seen cool however the main feature of cellars
is the ability to maintain a constant temperature with a minimum of
effort. Coober Pedy in South Australia (See:
http://www.opalcapitaloftheworld.com.au ) is a modern example of a
town built below ground to beat temperature variation as humans have
done since before recorded history.

When I was young, I went on a few spelunking trips in the summertime.
One of the most notable thing about caves is the pleasant coolness.
Even on a sweltering hot day, you'll feel cool (sometimes chilly) once
you get underground.

I nearly forgot the water temperature in the pipes. Whatever the
temperature of the water at it's starting point (river, water tank,
dam or reservoir) the longer it is in the pipes under the ground the
closer the temperature will become to the temperature of the
surrounding soil. If the soil temperature is 50-55 and the water
temperature at it's source starts below 50-55 it will tend to absorb
heat from the surrounding soil and increase towards 50-55. If it
starts above 50-55 it will loose heat and tend to decrease towards
50-55.

I understand why nassim99 is asking. I lived in Seattle most of my
life where you turn on the tap and wait for the hot water to get hot.
Cold is already cold. Then, I mo=ved to Las Vegas and lived there for
6 years, --what a difference! In LV, the hot is always ready to go,
but when you turn on the cold tap, you have to wait for it to turn
from hot to cold.

Well below ground the temperature is approximately the average of the
surface temperature, so it is cooler than the hot days of summer and
warmer than the coldest periods of the winter. In artic regions it can
be below freezing, hence permafrost. In tropical regions it can be
well above the 50-55 F degrees mentioned in the first comment.
Of course, it is very hot at the center of the earth, so there is a
constant flow of heat to the surface. This creates a thermal gradient
that depends on the thermal conductivity of the bedrock (how good an
insulator it is). A typical value would be about 30 degrees Centigrade
per kilometer, so if you are less the 10 meters below the surface, the
contribution from this would be only a fraction of a degree. If you
several kilometers down at the bottom of a deep mine, it would be very
hot!

Nassim,
The pipes are likely within a couple feet of the surface of the
ground. This means they are still somewhat affected by the outside
temperature.
Even if they are deeper, the temperature will be about 55 degrees.
This is not at all cool compared to the ice cold 32 degree water you
are used to drinking... that is why it does not seem cool.

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